1. Field of the Invention
The invention relates to robots used for substrate transport in semiconductor processing.
2. Description of the Related Art
Robots are commonly used in semiconductor processing environments, in order to transport substrates such as wafers to and from storage locations or various processing stations. The highly repetitive nature of the motions involved and the speeds required for high throughput make robots ideal candidates for these tasks. The types of motions of which these types of robots are capable vary. Typically, a robot 451 shown in FIG. 13, which has a robot body 453 and a robot arm 455 extending from the robot body will exhibit angular (θ), radial (R) and Z motions in a cylindrical coordinate system. As seen in FIG. 13, angular motion refers to rotation of the robot arm 455 about a primary axis 457 at which it is pivotably coupled to the robot body 453. Radial motion is extension/retraction motion of the robot arm 455 to and from the primary axis. Z motion is elevation of the robot arm 455 with respect to the robot body 453. Z motion is achieved by extending or retracting shaft 459 to which arm 455 is mounted out of or into robot body 453. Details of operation of such robots are described in U.S. Pat. No. 5,789,890, entitled “ROBOT HAVING MULTIPLE DEGREES OF FREEDOM” (Genov et al.).
Issues that are of concern in these types of robots include weight, size, complexity, and range. The present invention seeks to address one or more of these issues, to thereby improve factors such as robot performance, reliability, and throughput, and to increase longevity and reduce costs of robot manufacture and maintenance.
With respect to the issue of range, it will be appreciated that industry standards require that in an operating environment, 300 mm wafers storage cassettes, from which the robot 451 must retrieve the 300 mm wafers, must be disposed at a height of 900 mm. This imposes limitations on the robot height, which translate to limitations on robot range in the Z direction. When longer Z travel is required, one of two approaches has conventionally been implemented. The first approach, shown in FIG. 14, is to mount the robot 451 on an additional vertical translation module 461. This retains the ability of the robot to be dimensioned so as to reach the 900 mm high cassettes and to have the usual Z motion range provided by shaft 459 (FIG. 13), and would further augment that range by the additional travel permitted by vertical translation module 461. However, the translation module 461 is very heavy and cumbersome, and introduces significant amounts of inertia to the system. One reason for this is that typically such a module relies on a ball screw 475, which itself is heavy difficult to manipulate. The use of the translation module 461 therefore detracts from system speed, longevity, and overall performance while raising its cost and complexity. The second approach, shown in FIG. 15, is to provide a robot having telescoping ability. Robot 463 is shown having a plurality of vertically stacked, movable platforms 465, 467, 469, on which robot arm 471 is mounted. The platforms are supported on movable supports 473 that, in the retracted position, occupy a minimal amount of space in the Z dimension. Nonetheless, such an arrangement remains fairly constrained in its range, and requires expansion in the radial direction (R) to accommodate the additional collapsible supports 473, and is therefore cumbersome and tremendously complex.